Oxenstierna was a strong supporter of monarchical power.
Despite his status as Sweden’s leading nobleman, he did not share the views of
other noblemen who viewed an extension of monarchical power as being at their
expense. Though he had been responsible for the Accession Charter which the
young Gustavus had to sign in 1611, he was a monarchist.

When Gustavus was killed at Lutzen in 1632, Oxenstierna
assumed supreme command of Sweden’s forces in the Thirty Years
War. He worked
with considerable energy but he faced major problems - Sweden was running short
of money; the German Protestant alliance was becoming increasingly difficult to
maintain; Oxenstierna was mindful of Richelieu in France who he believed was
trying to turn Sweden into a puppet of France. Oxenstierna also had to contend
with some headstrong generals such as General Horn, Johan Baner and Karl Gustav
Wrangel. That Oxenstierna kept these problems at a controllable level is a
testament to his natural abilities.

The Treaty of Westphalia is a testament to Sweden’s
standing in Europe by 1648. Sweden acquired West Pomerania including Stettin and
the Oder Estuary, Wismar in Mecklenburg and the bishoprics of Bremen and Verdun.
Sweden also got 5 million thalers from the settlement.

During the regency of Christina, Oxenstierna ruled Sweden.
His Regency of Five included one of his brothers and a cousin. This way there
was always a majority in the Five who would support Oxenstierna.

In July 1634, Oxenstierna drew up the Form of Government
which completely modernised Sweden’s administration. Christina was highly
suspicious of this document as she saw it as potentially expanding Oxenstierna’s
power at her expense. Christina became convinced that Oxenstierna was taking
advantage of her youth and sex.

In 1636, Oxenstierna returned to Sweden from Germany where
he had been directing Sweden’s input into the Thirty Years
War. It is from
this time on that the relationship between Oxenstierna and Christina started to
weaken. In 1644, Christina came of age and she started to assert her authority
which could only impact the authority Oxenstierna had acquired. As a supporter
of monarchical power, he could hardly complain about what Christina was doing.
1644 to 1654 is sometimes referred to as the "Ten Year Rule" - a
reference to Christina asserting her authority and making decisions for her
country at the expense of Oxenstierna.

The main source of conflict was the issue of who should
succeed Christina. She had set her heart on marrying Charles Gustav. When it
became obvious that this was not to be, she made it clear that she would not get
married but that Charles Gustav was to be her successor. Oxenstierna believed
that the government had a right to be consulted on such an important issue - a
view not shared by Christina.

The Council’s main concern was that Christina was
breaking down the working relationship that had developed when Gustavus was king
of Sweden. Oxenstierna believed that her approach might push Sweden towards
absolute monarchical rule and that a breakdown in trust would occur. They were
also concerned that there was no obvious proof that Charles was a suitable
candidate for Sweden’s throne.

Another issue that was getting between the crown and the
nobility was the issue of resumption. This was the name given to the process
whereby the monarchy attempted to buy back former royal land it had sold cheaply
to the nobility so that the Thirty Years War could be adequately funded. Many
noblemen had benefited from this sale and now jealously guarded what they
believed was legally theirs.

Christina knew that if she appeared to be moving towards
the lower estates, that would concern the numerically much smaller nobility of
Sweden. In 1650, the lower estates via the Diet demanded resumption and also a
limitation being put on noble power.

Christina supported this and used this support to get the
nobles to agree to her choice of successor. When the nobles agreed to her
choice, she returned to their side though a law was passed in 1652 which limited
the extra labour a free peasant could do on ex-royal land. However, this was
very minor compared to what the nobility had feared could be passed. After this,
the normal relationship between crown and nobles was restored. Christina had
asserted her power and Oxenstierna had to accept this.

From 1652 to his death in 1654, both resumed a ‘normal’
relationship. By the time of his death, Oxenstierna had at least maintained
noble power within Sweden - no mean achievement considering the complexity of
the circumstances he worked in.